OF ARTS AND SCIENCES. 



195 



the region of active growth at the base, as do most of the hairs iu the 

 Pha:ospure(e. 



In the series of sections the first evidence of an increase in com- 

 plexity is shown in Figure 12. In this transverse section it will be 

 seen that two cells, at A and A, have divided by walls parallel to the 

 surface of the frond, and that these two cells are not situated side 

 by side, but are separated by one cell. Sections from other plants 

 represent the initial cells somewhat differently. In one case there was 

 a single one, and in another two were side by side. A section from 

 the same series as the one represented in Figure 12, and about 30 /x 

 below it, is represented in Figure 13. In this the process has gone 

 further, and the central portion of the blade is two-layered, while the 

 edges are only one-layered. A longitudinal section of a young blade 

 showed that in that particular specimen the two-layered portion was 

 five cells in height. Soon we come to a section such as that repre- 

 sented in Figure 14, where there is a third cell of different shape 

 and appearance in the centre, and the two layers are separated from 

 each other in the middle to make room for it. This cell lacks the 

 chromatophores, is round in cross-section, and has a lining of dense 

 protoplasm, in which are embedded numerous small nuclei, which take 

 on a deep stain with ha^raatoxylin. 



In the same figure will be noticed two groups of hairs, one project- 

 ing from each surface. E)ach group seems to have arisen in this case 

 from the divisions of a single cell. • In the several-layered blade they 

 are frequently opposite in this fashion. 



Figure 15 is drawn much less magnified, and the cells are all repre- 

 sented on one side to show the proportions existing between the many- 

 layered and the one-layered portions of the blade. It will be seen 

 here that there are three of the central cells in this section. In 

 longitudinal section these central cells appear as elongated tubes, the 

 ends of which are not readily found. They will be spoken of as 

 tubes, or tubular cells, for the present. 



Figure 16 shows a section still lower in the original series. The 

 many-layered portion is wider, and the cells appear irregularly placed ; 

 but the arrangement is seen better in Figures 17 and 18, still lower 

 down. The tubular cells are readily seen at a and A. The many- 

 layered blade, about half of which is represented in the figures, has 

 increased chiefly \\\ width. At B in Figure 17 is seen a group of four 

 cells, situated apart in the one-layered portion, which recalls the state 

 of things represented in Figure 12, and looks as if the cells were the 

 initial cells of a new many-layered portion. Such is the case in fact. 



